Appendix A. fakeroot 1.2.3 manual page

fakeroot(1)                      Debian manual                     fakeroot(1)



NAME
       fakeroot  -  run a command in an environment faking root privileges for
       file manipulation

SYNOPSIS
       fakeroot [-l|--lib library] [--faked faked-binary] [-i  load-file]  [-s
       save-file]   [-u|--unknown-is-real   ]  [-b|--fd-base  ]  [-h|--help  ]
       [-v|--version ] [--] [command]

DESCRIPTION
       fakeroot runs a command in an environment wherein it  appears  to  have
       root  privileges  for  file  manipulation.  This is useful for allowing
       users to create archives (tar, ar, .deb etc.) with files in  them  with
       root  permissions/ownership.   Without  fakeroot one would need to have
       root privileges to create the constituent files of  the  archives  with
       the  correct  permissions  and ownership, and then pack them up, or one
       would have to  construct  the  archives  directly,  without  using  the
       archiver.

       fakeroot  works  by  replacing  the file manipulation library functions
       (chmod(2), stat(2) etc.) by ones that  simulate  the  effect  the  real
       library  functions would have had, had the user really been root. These
       wrapper functions are  in  a  shared  library  /usr/lib/libfakeroot.so*
       which is loaded through the LD_PRELOAD mechanism of the dynamic loader.
       (See ld.so(8))

       If you intend to build packages with fakeroot, please try building  the
       fakeroot  package first: the "debian/rules build" stage has a few tests
       (testing mostly for bugs in old fakeroot versions). If those tests fail
       (for  example  because you have certain libc5 programs on your system),
       other packages you build with fakeroot will quite likely fail too,  but
       possibly in much more subtle ways.

       Also,  note that it's best not to do the building of the binaries them-
       selves under fakeroot. Especially configure and friends don't  like  it
       when  the  system  suddenly  behaves differently from what they expect.
       (or, they randomly unset some  environment  variables,  some  of  which
       fakeroot needs).


OPTIONS
       -l library, --lib library
              Specify an alternative wrapper library.

       --faked binary
              Specify an alternative binary to use as faked.

       [--] command
              Any  command  you want to be ran as fakeroot. Use '--' if in the
              command you have  other  options  that  may  confuse  fakeroot's
              option parsing.

       -s save-file
              Save  the  fakeroot  environment to save-file on exit. This file
              can be used to restore the environment later using -i.  However,
              this  file will leak and fakeroot will behave in odd ways unless
              you leave the files touched inside the fakeroot alone when  out-
              side the environment. Still, this can be useful. For example, it
              can be used with rsync(1) to back up and restore whole directory
              trees  complete  with user, group and device information without
              needing to be  root.  See  /usr/share/doc/fakeroot/README.saving
              for more details.

       -i load-file
              Load a fakeroot environment previously saved using -s from load-
              file.  Note that this does not implicitly save the file, use  -s
              as  well for that behaviour. Using the same file for both -i and
              -s in a single fakeroot invocation is safe.

       -u, --unknown-is-real
              Use the real ownership of files previously unknown  to  fakeroot
              instead of pretending they are owned by root:root.

       -b fd  Specify fd base (TCP mode only). fd is the minimum file descrip-
              tor number to use for TCP connections; this may be important  to
              avoid  conflicts  with the file descriptors used by the programs
              being run under fakeroot.

       -h     Display help.

       -v     Display version.


EXAMPLES
       Here is an example session with fakeroot.  Notice that inside the  fake
       root  environment  file manipulation that requires root privileges suc-
       ceeds, but is not really happening.

       $  whoami
       joost
       $ fakeroot /bin/bash
       #  whoami
       root
       # mknod hda3 b 3 1
       # ls -ld hda3
       brw-r--r--   1 root     root       3,   1 Jul  2 22:58 hda3
       # chown joost:root hda3
       # ls -ld hda3
       brw-r--r--   1 joost    root       3,   1 Jul  2 22:58 hda3
       # ls -ld /
       drwxr-xr-x  20 root     root         1024 Jun 17 21:50 /
       # chown joost:users /
       # chmod a+w /
       # ls -ld /
       drwxrwxrwx  20 joost    users        1024 Jun 17 21:50 /
       # exit
       $ ls -ld /
       drwxr-xr-x  20 root     root         1024 Jun 17 21:50 //
       $ ls -ld hda3
       -rw-r--r--   1 joost    users           0 Jul  2 22:58 hda3

       Only the effects that user joost could do anyway happen for real.

       fakeroot was specifically written to  enable  users  to  create  Debian
       GNU/Linux  packages  (in  the  deb(5)  format) without giving them root
       privileges.  This  can  be  done  by  commands  like  dpkg-buildpackage
       -rfakeroot  or  debuild  -rfakeroot (actually, -rfakeroot is default in
       debuild nowadays, so you don't need that argument).

SECURITY ASPECTS
       fakeroot is a regular, non-setuid program. It does not enhance a user's
       privileges, or decrease the system's security.

FILES
       /usr/lib/libfakeroot/libfakeroot.so*  The shared library containing the
       wrapper functions.

ENVIRONMENT
       FAKEROOTKEY
              The key used to communicate with the fakeroot daemon.  Any  pro-
              gram  started  with  the right LD_PRELOAD and a FAKEROOTKEY of a
              running daemon will automatically connect to  that  daemon,  and
              have  the same "fake" view of the file system's permissions/own-
              erships.  (assuming  the  daemon  and  connecting  program  were
              started by the same user).

LIMITATIONS
       Library versions
              Every command executed within fakeroot needs to be linked to the
              same version of the C library as fakeroot itself.

       open()/create()
              fakeroot doesn't wrap open(), create(), etc. So, if  user  joost
              does either

              touch foo
              fakeroot
              ls -al foo

              or the other way around,

              fakeroot
              touch foo
              ls -al foo

              fakeroot has no way of knowing that in the first case, the owner
              of foo really should be joost while the second  case  it  should
              have  been root.  For the Debian packaging, defaulting to giving
              all "unknown" files uid=gid=0, is always OK. The real way around
              this  is  to  wrap  open()  and create(), but that creates other
              problems, as demonstrated by the libtricks package. This package
              wrapped  many  more  functions,  and tried to do a lot more than
              fakeroot .  It turned out that a minor upgrade of libc (from one
              where the stat() function didn't use open() to one with a stat()
              function that did (in some cases) use open()), would cause unex-
              plainable  segfaults  (that  is,  the  libc6  stat()  called the
              wrapped open(), which would then call the  libc6  stat(),  etc).
              Fixing  them wasn't all that easy, but once fixed, it was just a
              matter of time before another function started  to  use  open(),
              never  mind  trying  to port it to a different operating system.
              Thus I decided to keep the number of functions wrapped by  fake-
              root  as  small  as possible, to limit the likelihood of 'colli-
              sions'.

       GNU configure (and other such programs)
              fakeroot, in effect, is changing the  way  the  system  behaves.
              Programs  that  probe the system like GNU configure may get con-
              fused by this (or if they don't, they  may  stress  fakeroot  so
              much  that fakeroot itself becomes confused). So, it's advisable
              not to run "configure" from within fakeroot. As configure should
              be   called   in   the   "debian/rules  build"  target,  running
              "dpkg-buildpackage -rfakeroot" correctly takes care of this.

BUGS
       It doesn't wrap open(). This isn't bad by itself, but if a program does
       open("file", O_WRONLY, 000), writes to file "file", closes it, and then
       again tries to open to read the file, then that open fails, as the mode
       of  the file will be 000. The bug is that if root does the same, open()
       will succeed, as the file permissions aren't checked at all for root. I
       choose not to wrap open(), as open() is used by many other functions in
       libc (also those that are already wrapped),  thus  creating  loops  (or
       possible  future  loops,  when the implementation of various libc func-
       tions slightly change).

COPYING
       fakeroot is distributed under the GNU General Public License.  (GPL 2.0
       or greater).

AUTHORS
       joost witteveen
              <joostje@debian.org>

       Clint Adams
              <schizo@debian.org>

       Timo Savola

MANUAL PAGE
       mostly  by  J.H.M.  Dassen <jdassen@debian.org> Rather a lot mods/addi-
       tions by joost and Clint.

SEE ALSO
       faked(1) dpkg-buildpackage(1), debuild(1) /usr/share/doc/fakeroot/DEBUG




Debian Project                   6 August 2004                     fakeroot(1)